Fertilizer for Olive Trees

Olive trees need moderate amounts of nitrogen for good growth.

Tough, drought-resistant, adaptable, long-lived, hardy -- all these terms characterize olive trees (Olea europaea). Native to the Mediterranean area, olive trees are adapted to grow on poor soil yet still produce fruit. They don't require high fertilizer levels to grow well; too much fertilizer can actually harm crop production and oil quality. Olives grow best if they are fed throughout the growing season, with the main need being nitrogen. Olives grow in U.S. Department of Agriculture hardiness zones 9 through 11.

Kinds of Fertilizers

Organic and chemical fertilizers each benefit olive trees. Organic fertilizers, such as compost and aged animal manure, supply trees with a fertilizer source that decomposes over an extended time and helps amend the soil. Many European growers fertilize olive trees with organic fertilizer every other year. Chemical fertilizers address immediate growing needs or nutritional deficiencies very quickly. Controlled release fertilizers give olive trees adequate fertilizer coverage for several months. Liquid fertilizers give immediate results but have to be repeated on a regular basis during the growing season; follow manufacturer's directions.

Nitrogen Fertilizers

Nitrogen is the one nutrient an olive tree may be deficient in. It is needed for formation of flowers, fruit and leaves. During spring growing season, for mature trees, give each tree 2 pounds of urea or 50 pounds of compost. For young trees, give 1 ounce of urea each month and water it in well. Other chemical formulations, such as ammonium nitrate, ammonium sulfate, calcium nitrate, or ammonium phosphate, have varying proportions of nitrates or ammonia for the nitrogen source and have different application rates. Consult your county agent for proper application rates. It's best to divide the total yearly amount a tree needs over the months of the growing season rather than apply too much at once.

Phosphorus, Potassium and Trace Elements

It is unlikely that olive trees would be deficient in either phosphorus or potassium. Olive trees don't need as much of these elements as other types of fruit-bearing trees. When using organic fertilizers, the olive tree usually gets all the potassium it needs. Unless soils are very poor, olives usually have satisfactory levels of secondary and trace elements like copper, zinc, manganese, magnesium and calcium. Paul Vossen, in his book on organic olive production, notes that California olive trees are unknown to be deficient in these minerals or in phosphorus. Limited local instances of boron deficiencies have occurred.

Application

Fertilizers should be applied to the top of the ground beneath the tree branches, but not close to the trunk. Water fertilizers in after application or time application just before significant rain. Foliar sprays don't give as effective results as fertilizer taken up by the roots. When deficiencies are severe, use foliar sprays for immediate results plus long-lasting ground applications to correct the problem. Avoid using formulations high in nitrogen meant for fast vegetative growth. Olive trees don't grow during cool winter months, so fertilizer isn't needed during this time.

Analyzing Deficiencies

To know which fertilizer olive trees need, send tissue samples from olive leaves to a laboratory for analysis. Samples should be taken in July, when nutrient levels are most stable. Some soils, such as those high in clay, retain nitrogen and yearly application isn't needed. If an olive tree isn't growing well, don't just give it fertilizer as a sort of magic bullet. First find out what else could be wrong, since olives are seldom nutrient-deficient. Often olives need more water or better drainage. They also could need to have weeds or nearby plants controlled so they don't compete with the olive for food and water.

About the Author

Cathryn Chaney has worked as a gardening writer since 2002. Her horticultural experience working in the nursery industry informs her garden articles, especially those dealing with arid landscaping and drought-tolerant gardening. Chaney also writes poetry, which has appears in "Woman's World" magazine and elsewhere. Chaney graduated from the University of Arizona in 1992 with a Bachelor of Arts in English.